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Based on Discover God’s Creation
Chapter 6
By Rebecca Fraker
6-1 Erosion Caused By Water
Raindrops splashing on the
ground can move an amazing
amount of soil and rock.
In a single storm, raindrops
falling on an area the size of a
football field can move more
than 100 tons of dirt!
Ground Water
Ground water is precipitation, rain or melting
snow, that soaks into the soil.
Water drains through the soil until it reaches
solid rock.
There it collects into underground deposits
called the aquifer.
In some areas, water from the aquifer bubbles
up through the ground in springs.
In other areas, wells must be dug to tap into
the aquifer.
Erosion underground
• Erosion can occur
underground. In some
areas, water moves through
the soil and dissolves soft
rock. The dissolved
minerals are carried away,
leaving cracks and
openings.
• As water continues to
dissolve the rock, the cracks
and openings dissolve into
caves and caverns.
Sinkholes
• Some underground caves collapse because
they cannot support the weight of the ground
above them.
• This forms a sinkhole.
• Some sinkholes are
caused by natural erosion.
Others happen where too
much water or oil has been
pumped out of the ground.
Hot Spring
• If water flows down deep cracks and goes
inside the earth, it may get near hot
magma.
• If it does, it heats up. Then it may flow up
and out. This is a hot spring.
Geyser
• If the underground
heated water shoots
out of the ground with
a lot of force, it is
called a geyser.
• Some geysers are so
powerful, they spray
hot water and steam
400 feet in the air.
Runoff Water
• Most erosion is caused by runoff water.
• Runoff water is the water that does not
soak into the ground, but runs off the top
of the land downhill to form creeks and
streams.
• Streams combine to form rivers that
eventually empty into the ocean.
Load
• As runoff water moves over the land,
erosion takes place and the water picks up
soil, gravel, mud, humus, and rocks.
• This eroded material is called the load.
• As the river slows, the boulders and gravel
begin to settle out. Pebbles are deposited.
• Sand and mud are the last to sink to the
bottom and may often form sandbars.
Flood Plain
• When a river overflows its banks, the load
spreads over a large area called a flood
plain.
• Many towns and cities will not allow
people to build houses on flood plains.
• Other areas allow it. These places often
become the scenes of disasters, as we
saw recently in New Orleans. There,
many houses were built on the flood plain.
Alluvial fans
• Where rivers flow out of hills and
mountains into open valleys or plains,
alluvial fans form.
• Alluvial fans are fan-shaped deposits of
rocks and gravel at the base of hills or
mountains.
Delta
• By the time a river reaches the ocean, its
load usually consists of only very fine
particles. These tiny particles settle out at
the mouth of the river and form a delta.
• The Mississippi River deposits an average
of 850,000 tons of material at its delta
every day.
Ocean Waves
• Ocean waves cause erosion as they
hit the shore.
• The waves move material from one
place and deposit it in another,
forming different features.
• Ocean waves release tremendous
amounts of energy that can move
huge rocks.
• During one storm, a wave near Tillamook,
Oregon, hurled a 130 lb. Boulder 99 feet
above the shore and through the roof of a
building.
• The Mississippi River
delta continues to grow
out into the Gulf of
Mexico at a rate
of 350 feet a year.
Erosion Caused by Wind and
Gravity
• Wind erodes the land in two ways. One
way is by scooping out loose material
and blowing it away.
• The other way is similar to sandblasting.
Tiny grains of sand bombard rock
surfaces and slowly wear away softer
rock.
Deposits made by wind action
The world’s largest sand dunes are
in the Sahara desert.
• Sand dunes form in
deserts and along beaches
because of the wind.
• Often, sand is moved a
great distance. Sand
dunes on the shores of
Lake Michigan move 16-25
feet a year.
• Particles of rock and soil
carried by the wind grind
against each other, often
forming an even finer
powder.
Gravity
• As weathering takes place, gravity pulls
the loosened material down. Rock and
soil fall from cliffs or roll down steep
hillsides, gradually building up at the base.
Landslides/Rockslides
• Sometimes water so
saturates the ground
that the mud or rocks
on the side of a hill will
slip off in a highly
dangerous destructive
landslide or rockslide.
Earthquakes can also
trigger landslides.
6-3 Erosion Caused By Glaciers
• Glaciers are large masses of thick ice that move
slowly over the land.
• They form only in very high mountains or in cold
regions near the North and South poles, where
the temperatures never rise enough to melt the
snow completely.
Glaciers
• Year after year, snow builds up and
packs into ice.
• Large glaciers begin to move slowly over
the land, usually only a few meters per
year.
• However, the ones that are near the sea
move much faster because the land’s
surface near the sea is warmer.
Mendenhall Glacier in Alaska moves up
to 90 feet a day!
Two types of glaciers
• Continental glaciers
• Valley glaciers
Continental Glaciers
• These are large enough to cover most of
an entire continent.
• Today there are only two: one covering
most of Greenland, and one covering
Antarctica.
Valley Glaciers
These are much smaller
than continental glaciers.
Over 200,000 of these small glaciers are
scattered over Earth. Valley glaciers
usually occur in high mountains and look
like frozen rivers.
What do glaciers do?
• You can see the effects of glaciers throughout
much of Canada and the United States
• As glaciers move, they carve and grind away the
landscape like giant bulldozers, scraping away
soil and loose rocks and depositing it elsewhere.
• Moraines, eskers, glacial polish, erratic
boulders, and U-shaped valleys all indicate
where glaciers have come and gone.
Moraines
• As a glacier moves, long piles of rock and
soil called moraines, form along its edges.
• When the glacier melts, these moraines
remain.
• Sometimes they dam rivers and form
moraine lakes.
Eskers
• Water melting off the
glacier forms channel
beneath the ice.
• As water continues to
flow along these
channels, long winding
ridges called eskers
form.
Kettle Lakes
• Some glaciers gouge
out basins as they
move.
• When glaciers melt,
the basins fill with
water to form kettle
lakes.
• The state of
Minnesota, called the
“the land of 10,000
lakes” is dotted with
thousands of kettle
lakes.
Erratic Boulders
• As a glacier moves, it often picks up large
boulders and carries them to a new
location. When the glacier melts, it leaves
these erratic boulders behind.
Glacial Polish
• As glaciers move over some kinds of rock,
the grinding action “polishes” the surface
of the rock. These rocks shows glacial
polish.
U-Shaped Valleys
• As glaciers move between mountains,
they gouge out U-shaped valleys.
Yosemite Valley in California is an
example of this feature of glacial
action.